The ability to mount an effective immune response to pathogens requires a functional innate immune system. The innate immune system provides the first line of defense against infection. Toll-like receptors (TLR), a collection of membrane bound receptors found on many cells of the innate system, are molecules that drive important signaling pathways mediating the innate immune response. The importance of TLRs is highlighted by studies employing mice where components of the TLR signaling pathway are deleted. Loss of TLR signaling severely compromises innate immune responses and renders the host highly susceptible to infection. During the past year, several laboratories, including our own, have shown that TLR signaling, in addition to activating NF-kB and MAPK pathways, also activates the Notch signaling pathway. In this application, we propose that Notch activation, a newly described and novel target of TLR signaling, also influences innate immunes responses to the pathogen Borrelia burgdorferi. The experiments proposed in this application are designed to unravel the mechanism by which TLR signaling leads to Notch activation and may suggest novel drug targets for modulating immune responses. A second and equally important component of this application is to foster research partnerships between NIH-supported scientists (Osborne) and collaborators in the developing world (Palaga). The aims of this proposal are designed to extend an important and novel observation made by the LMIC investigator and the PI and to enhance research environment at the LMIC site as well as train an LMIC student in the PI's laboratory. The overarching goal of this application is to utilize our novel preliminary data to promote scientific collaboration and exchange between the two laboratories. Although Borrelia is not a pathogen endemic to the LMIC site, Thailand, Borrelia signals through TLR2, a signaling pathway used by many pathogens endemic in Thailand. Our studies proposed in this application will provide a framework for the LMIC investigator to investigate the role of Notch signaling in response to these pathogens. The research in this application will be conducted, in part, at Chulalongkorn University, Bangkok, Thailand and directed by Dr. Tanapat Palaga. This project is linked to parent grant PO1 AG025531, Barbara A. Osborne, PI (7/1/06-6/30/11). PUBLIC HEALTH RELEVANCE: The aims of this application will describe novel mechanisms that mediate the innate immune response to pathogens. Innate immune responses are critical for the clearance of most pathogens. Therefore studies that provide insight into these processes have high impact on human health. This application will be conducted in conjunction with an LMIC investigator at Chulalongkorn University in Bangkok, Thailand and will aid research efforts and training of students at the LMIC institution.